Abstract: In this paper the effect of the chemical structures of various drugs such as dextromethorphan hydrobromide(DM), pseuoephedrine hydrochloride(PE) and phenylpropanolamine hydrochloride(PM) on the exchange behavior with the strongly acidic cation exchanger(0017) was described. From experiments, it indicates that the exchange rate constants were found to be 1.041×10^-3±2.56×10^-5, 2.290×10^-2±1.24×10^-4, 2.40×10^-2±1.02×10^-4min^-1at 25℃ respectively. The K_eis increased with increasing temperature. The exchange activation energies were calculated to be 50.26, 21.68, 20.83 kJ 5mol^-1, respectively. The apparent equilibrium constants(K_e) were calculated to be 3.235±0.252, 3.680±0.214, 4.510±0.328 at 25 , respectively. The exchange reactions are spontaneous according to the data of G=-2.909±0.0205, -3.228±0.0181, -3.732±0.0127 kJ 5mol^-1, respectively. The reaction enthalpy H were found to be 88.44±5.548, 48.29±3.214, 48.66±3.158 kJ 5mol^-1, respectively, indicating the reaction is enthermal reaction.

Key words: Dextromethorphan hydrobromide, Pseuoephedrine hydrochloride, {Phenylpro-panolamine hydrochloride, Exchange reaction kinetics, Exchange reaction thermodynamics